1. Field of the Invention
The present invention relates to a method for producing a sulfur-containing amino acid such as L-cysteine, or a related substance thereof. Specifically, the present invention relates to a bacterium suitable for producing a sulfur-containing amino acid or a related substance thereof, and a method for producing a sulfur-containing amino acid or a related substance thereof utilizing such a bacterium. Sulfur-containing amino acids and related substances thereof are used in the fields of drugs, cosmetics, and foods.
2. Brief Description of the Related Art
L-cysteine is conventionally obtained by extraction from keratin-containing substances such as hair, horns, and feathers, or by conversion of the precursor DL-2-aminothiazoline-4-carboxylic acid with a microbial enzyme. L-cysteine has also been planned for production on a large scale by the immobilized enzyme method utilizing a novel enzyme. Furthermore, it has also been attempted to produce L-cysteine by fermentation utilizing a microorganism.
Microorganisms that are able to produce L-cysteine are known, for example, a coryneform bacterium with increased intracellular serine acetyltransferase activity (Japanese Patent Laid-open (Kokai) No. 2002-233384). Increasing L-cysteine-producing ability by incorporating a mutant serine acetyltransferase which is attenuated to L-cysteine feedback inhibition has also been reported (Japanese Patent Laid-open (Kokai) No. 11-155571, U.S. Patent Published Application No. 20050112731, and U.S. Pat. No. 6,218,168).
Furthermore, microorganisms which are able to produce an enhanced amount of L-cysteine by suppressing the L-cysteine decomposition system include coryneform bacteria, or Escherichia bacteria in which the activity of cystathionine-β-lyase (Japanese Patent Laid-open (Kokai) No. 11-155571), tryptophanase (Japanese Patent Laid-open (Kokai) No. 2003-169668), or O-acetylserine sulfhydrylase B (Japanese Patent Laid-open (Kokai) No. 2005-245311) is attenuated or deleted.
Furthermore, the ydeD gene encoding the YdeD protein is known to participate in secretion of the metabolic products of the cysteine pathway (Dassler et al., Mol. Microbiol., 36, 1101-1112 (2000)). Other known methods of enhancing L-cysteine-producing ability include increasing the expression of the mar-locus, emr-locus, acr-locus, cmr-locus, mex-gene, bmr-gene, or qacA-gene (U.S. Pat. No. 5,972,663), or emrAB, emrKY, yojIH, acrEF, bcr, or cusA gene (Japanese Patent Laid-open (Kokai) No. 2005-287333). These loci/genes encode a protein suitable for excreting a cytotoxic substance.
Another known L-cysteine-producing bacterium is Escherichia coli in which the activity of the positive transcriptional control factor of the cysteine regulon encoded by the cysB gene is increased (International Patent Publication WO01/27307).
Furthermore, a mutant serA coding for 3-phosphoglycerate dehydrogenase with attenuated feedback inhibition by serine, and the use thereof for L-cysteine production by Escherichia coli has been suggested (U.S. Pat. No. 5,856,148 and U.S. Patent Published Application No. 20050009162).
Methionine is industrially produced mainly by chemical synthesis as a mixture of D- and L-isomers. When the L-isomer is required, it can be produced by acetylating the D- and L-isomers to convert them into N-acetyl-DL-methionine, and enzymatically deacetylating only the L-isomer. Production of L-methionine by fermentation has also been attempted using a microorganism. As L-methionine-producing bacteria, Escherichia coli bacteria have been reported that are deficient in the repressor of the L-methionine biosynthesis system, and which have enhanced intracellular homoserine transsuccinylase activity, attenuated intracellular S-adenosylmethionine synthetase activity, L-threonine auxotrophy, enhanced intracellular cystathionine γ-synthase activity, and enhanced intracellular aspartokinase-homoserine dehydrogenase II activity (U.S. Pat. No. 7,611,873), and so forth.
The yeeE gene is registered in the database EcoCyc (BioCyc Home Page, Escherichia coli K-12 substr. MG1655 Gene: yeeE [searched on Jul. 13, 2010], Internet URL biocyc.org/ECOLI/NEW-IMAGE?type=GENE&object=EG11895) as a gene coding for a putative transport system permease protein. Furthermore, according to an analysis using the membrane protein prediction program SOSUI (bp.nuap.nagoya-u.ac.jp/sosui/sosui_submit.html), YeeE is predicted to be a nine-transmembrane protein. Therefore, YeeE is presumed to be a type of transporter, but the actual functions are unknown. Furthermore, the relation of YeeE to production of sulfur-containing amino acids has not been reported.
Furthermore, the yeeE gene has been reported to be up-regulated by cadmium (Kerstin et al., J. Bacteriol., Aug. 2008, 190:5439-5454), by zinc (Kaneyoshi et al., J. Bacteriol., Sep. 2005, 187:6333-6340), by CORM-2, which is a CO-discharging agent (Ligia S., Nobre et al., Microbiology, Mar. 2009, 155:813-824), at an early stage of the stationary phase in an RpoE-dependent manner (Md. Shahinur Kabir et at, Microbiology, August 2005, 151:2721-2735), and at a temperature of 37° C., which is the human body temperature (Christine A. et at, J. Bacteriol., Aug. 2007, 189:5429-5440). The yeeE gene has also been reported to be down-regulated by acetic acid (Carrie N. Arnold et al., J. Bacteriol., Apr. 2001, 183:2178-2186), by ursolic acid (Dacheng Ren et at, Appl. Envir. Microbiot, Jul. 2005, 71:4022-4034), and in the IHF(−) strain (Stuart M. Arfin et al., J. Biol. Chem., Sep. 2000, 275:29672). However, in the literature, the yeeE gene is only mentioned as one of many genes that show change of expression in microarray experiments, and the relation of this gene with production of sulfur-containing amino acids has not been suggested or reported.